EP3290966A1 - Anti-reflective optical surface, structured and with long durability, and method for manufacturing same - Google Patents

Abstract

An antireflection optical surface, with visible and near infrared absorption, comprises a substrate (4) made of SiC silicon carbide material and a microstructure assembly (8) (12, 14, 16, 18, 20, 22) lining an exposure face (6) of the substrate (4). Each microstructure (12, 14, 16, 18, 20, 22) is formed by a single protuberance disposed on and in one piece with the substrate (4). The microstructures (12, 14, 16, 18, 20, 22) have the same shape and dimensions, and are distributed on the face (6) of the substrate (4) in a two-dimensional periodic pattern, and the shape of each microstructure ( 12, 14, 16, 18, 20, 22) is smooth and regular with a radius of curvature that varies continuously from the top of the microstructure to the face (6) of the substrate (4).

Description

The present invention relates to a structured antireflection surface on a SiC-based silicon carbide material.

The present invention particularly relates to an optical surface with high absorption in the visible range and reduced emissivity that can serve as a solar absorber.

The present invention also relates to a ceramic solar absorber of the silicon carbide type, used on a solid SiC silicon carbide material or as a SiC absorber layer deposited on the surface of another material, for example steel, constituting by example a solar receiver. This is the main application of this invention.

The solar absorbers known to date use volume-structured silicon carbide or structured surfaces in a material different from silicon carbide or interferential deposits obtained from materials different from silicon carbide.

A first document by F. Gomez-Garcia, titled "Thermal and Hydrodynamic Behavior of Ceramic Volumetric Absorbers for Central Solar Receiver Power Plants: A Review", published in Renewable and Sustainable Energy Reviews 57 52016, 648-658, describes a solar absorber. silicon carbide structured in its volume in the form of a porosity in which solar radiation is partially trapped.

A second paper, the article by YM Song et al., Entitled "Antireflective grassy surface on glass substrates with self masked dry etching," published in Nanoscale Research Letters 2013, 8: 505, describes the principle of a plasma etching process. which generates by its chemistry a micro-masking, which micro-masking slows the etching of the substrate material in places. This results in a microstructure having relatively high aspect ratios that reduce the reflectivity of the surface. The approach described in this document only concerns glass and is not directly transferable to silicon carbide. The structures produced here by this method are smaller than those achieved in our patent proposal.

A third document, the article of J. Cai et al., Entitled "Recent advances in antireflective surfaces based on nanostructure arrays", published in Royal Society of Chemistry, Material Horizons 2015, 2, pages 37-53. , describes a first method for producing pseudoperiodic structures, this time on SiC silicon carbide for LED light electroluminescent diode (LED) applications. The conical structures obtained by this method are produced by etching through a metal mask obtained by dewetting thin layers. Reflectivity at 6 degrees of incidence over the spectral range from 390 to 785 nm is reduced from 20.5% to 1.62%. The same article mentions a second method for producing microstructures by plasma etching a silicon Si substrate through a polystyrene bead mask. This second method is limited here to the etching of a silicon substrate and does not describe the development of a form of microstructures particularly resistant to oxidation.

Like the third document, the patent application WO 2013/171274 A1 , forming a fourth document, describes a method of micro-masking etching, the micro-masking being carried out by dewetting of metals, and describes a micro-structured surface made on substrates of silicon carbide SiC or gallium nitride GaN for obtain an anti-reflective function. This micro-structured surface fabrication process is achieved by plasma etching through metal nano-islands of 10 to 380 nm in diameter and separation distances. The islands are made of metals including silver, platinum, aluminum, palladium. The base of the cones is less than 400 nm. In a first embodiment, the gold nano-islands are formed from a three-minute anneal at 650 ° C. of a gold layer with a thickness of 3 to 11 nanometers. In a second embodiment, the nano-islands are formed from a 33 minute anneal at 650 ° C on a gold layer 13 to 21 nanometers thick. The characteristic dimensions of the microstructures obtained are thus small, less than one hundred nanometers. Moreover, the use of metal is generally not recommended in the manufacture of semiconductor devices for contamination and carrier mobility modification issues. In addition, this technique of dewetting of metal is sensitive to the types of materials used for the substrate, their mono or polycrystalline character, and the surface roughness of the substrate, which we seek to avoid.

Like the third document, the patent application WO 2015/114519 A1 , forming a fifth document, describes a method of structuring molybdenum using a plasma etching of a molybdenum substrate through a silica or polystyrene bead mask. The microstructures obtained described are for example of pyramidal shape, and have sharp edges, promoting the wear of the micro-structured surface when subjected to a corrosive environment. It is sought to improve the performance of the molybdenum absorbers thus obtained, especially their service life when these surfaces are subjected to a high temperature and an oxidizing environment such as air. Indeed, these molybdenum surfaces have a poor temperature under air because of its oxidation.

The technical problem is to provide antireflection optical surfaces for solar absorbers which have both a high solar radiation absorption capacity and a resistance of this capacity at high temperature and in an oxidizing medium such as air.

For this purpose, the subject of the invention is an antireflection optical surface with absorption in the visible and near infrared range, in particular for solar thermal absorbers, able to operate at high temperatures, and comprising a substrate consisting of a thickness of a first SiC silicon carbide material, and having a planar face or exposure curve, and a set of texturing microstructures lining the face. The optical antireflection surface is characterized in that each microstructure is formed by a single protrusion made in the first material, arranged on and in one piece with the substrate, and the microstructures have the same shape and same dimensions, and are distributed over the face of the substrate in a two-dimensional periodic pattern, and the shape of each microstructure is smooth and regular having a single peak and a radius of curvature which varies continuously from the top of the microstructure to the face of the substrate.

• .- le premier matériau à base de carbure de silicium est du carbure de silicium SiC monocristallin ou poly-cristallin, ou du carbure de silicium SiC monocristallin ou poly-cristallin, enrichi en silicium sous forme d'îlots de silicium Si ;
• .- la surface de chaque microstructure présente un même maximum en hauteur h situé dans une zone centrale et correspondant à la hauteur de la microstructure et décroit depuis le sommet vers un bord B d'une base de la microstructure ;
• .- la surface de chaque microstructure comporte une partie de la surface d'une calotte sphérique, elliptique ou parabolique ;
• .- chaque microstructure a sensiblement un même diamètre de base d supérieur ou égal à 0,3 µm et inférieur ou égal 5 µm, de préférence compris entre 0,5 µm et 2 µm, et la même hauteur maximale h de chaque microstructure est supérieure ou égale à 0,5 fois le diamètre de base d et inférieure ou égale à 1,5 fois le diamètre de base d ;
• .- le rayon de courbure de chaque microstructure est supérieur ou égal à 0,1 µm et distribué autour d'une valeur centrale de rayon de courbure comprise entre 0,25 µm et 1 µm ;
• .- l'agencement des microstructures sur la face d'exposition du substrat est réalisé sous la forme d'un pavage de réseaux élémentaires de microstructures, les réseaux élémentaires ayant un même motif de maille compris dans l'ensemble formé par les mailles hexagonales, les mailles carrés, les mailles triangulaires, et étant caractérisé par un degré de compacité des microstructures entre elles.

According to particular embodiments, the anti-reflective optical surface comprises one or more of the following characteristics:

• the first silicon carbide material is monocrystalline or polycrystalline SiC silicon carbide, or single crystal or polycrystalline SiC silicon carbide, enriched in silicon in the form of Si silicon islands;
• the surface of each microstructure has the same maximum height h located in a central zone and corresponding to the height of the microstructure and decreasing from the top to an edge B of a base of the microstructure;
• the surface of each microstructure comprises a portion of the surface of a spherical, elliptical or parabolic cap;
• each microstructure has substantially the same base diameter d greater than or equal to 0.3 μm and less than or equal to 5 μm, preferably between 0.5 μm and 2 μm, and the same maximum height h of each microstructure is greater than or equal to 0.5 times the base diameter d and less than or equal to 1.5 times the base diameter d;
• the radius of curvature of each microstructure is greater than or equal to 0.1 μm and distributed around a central value with a radius of curvature of between 0.25 μm and 1 μm;
• the arrangement of the microstructures on the exposure face of the substrate is in the form of a tessellation of elementary microstructure networks, the elementary arrays having the same mesh pattern included in the set formed by the hexagonal meshes, the square meshes, the triangular meshes, and being characterized by a degree of compactness of the microstructures between them.

The invention also relates to a solar absorber comprising an optical surface as defined above.

The invention also relates to a method of manufacturing an optical antireflection surface, in particular for solar thermal absorbers, able to operate at high temperatures. The manufacturing method comprises a first step of providing a substrate, consisting of a thickness of a first SiC silicon carbide material, and having a planar or curved exposure face. The manufacturing method is characterized in that it further comprises a second step, carried out following the first step, of producing a set of texturing microstructures, lining the face, each microstructure being formed by a single protrusion made in the first material, and disposed on and in one piece with the substrate, and the microstructures having the same shape and same dimensions, being distributed on the face of the substrate in a two-dimensional periodic pattern, and the shape of each microstructure being smooth and regular having a single vertex and a radius of curvature that varies continuously from the top to the face.

• .- la première étape consiste soit à fournir du carbure de silicium SiC monocristallin ou poly-cristallin, ou soit à fournir du carbure de silicium SiC monocristallin ou poly-cristallin, enrichi en silicium sous forme d'îlots de silicium Si ;
• .- la première étape consiste soit à comprimer de manière isostatique une poudre de carbure de silicium SIC, ou soit à faire croitre du carbure de silicium SiC poly-cristallin, ou soit à faire croitre du carbure de silicium SiC monocristallin, ou soit à infiltrer du silicium à haute température dans une matrice carbonée poreuse ;
• .- la deuxième étape comprend les étapes successives consistant à : dans une troisième étape déposer une monocouche compacte de particules en un deuxième matériau à la surface du substrat, et dans une quatrième étape graver par un procédé de gravure sèche le substrat du côté de la face d'exposition au travers d'interstices existant entre les particules, le deuxième matériau étant compris dans l'ensemble formé par la silice (SiO₂), le polystyrène (PS) ou tout autre matériau sous forme de billes de dimension requise ;
• .- une réduction de la taille et de la forme des particules par gravure sèche est mise en oeuvre, soit dans une cinquième étape exécutée pendant la quatrième étape en même temps que la gravure sèche du substrat, soit dans une sixième étape interposée entre la troisième étape et la quatrième étape ;
• .- le dépôt du film compact de particules mis en oeuvre au cours de la troisième étape est réalisé soit par une technique de dépôt faisant intervenir l'interface air/liquide pour ordonner les particules comprise dans l'ensemble formé par la technique de Langmuir Blodgett, la technique de Langmuir Shaefer, la méthode vortique de surface, la technique du transfert par flottaison, la technique de l'écoulement laminaire fin dynamique et mobile, soit par une technique de depôt faisant intervenir exclusivement des particules en solution colloïdale comprise dans l'ensemble formé par le dépôt électrophorétique, le dépôt horizontal par évaporation d'un film, le dépôt par évaporation d'un bain, le dépôt par retrait vertical d'un substrat immergé et le dépôt horizontal par retrait forcé de la ligne de contact ;
• .- le procédé de gravure sèche mis en oeuvre dans la quatrième étape est une gravure réactive ionique utilisant un mélange gazeux d'hexafluorure de soufre (SF₆) et de dioxygène (O₂) dans un rapport de 5/3 ;
• .- la vitesse de gravure du matériau substrat Vsub et la vitesse de gravure Vpar des particules, la sélectivité de gravure Sg, définie comme le rapport de la vitesse de gravure du substrat sur la vitesse de gravure des particules, et le temps de gravure sont réglés de façon à consommer la totalité des particules et éviter la création d'arêtes vives sur la surface du substrat ;
• .- le procédé de fabrication comprend une septième étape de retrait des particules exécutée après la quatrième étape.

According to particular embodiments, the method of manufacturing an optical antireflection surface comprises one or more of the following characteristics:

• the first step consists either of supplying monocrystalline SiC silicon or polycrystalline silicon carbide, or of supplying silicon carbide SiC monocrystalline or polycrystalline, enriched in silicon in the form of Si silicon islands;
• the first step consists either of isostatically compressing a silicon carbide powder SIC, or of growing polycrystalline SiC silicon carbide, or of growing monocrystalline SiC silicon carbide, or of infiltrating high temperature silicon in a porous carbon matrix;
• the second step comprises the successive steps consisting in: in a third step depositing a compact monolayer of particles into a second material on the surface of the substrate, and in a fourth step etching by a dry etching process the substrate on the side of the exposure face through interstices existing between the particles, the second material being included in the assembly formed by silica (SiO ₂ ), polystyrene (PS) or any other material in the form of beads of required size;
• a reduction in the size and shape of the particles by dry etching is carried out, either in a fifth step carried out during the fourth step at the same time as the dry etching of the substrate, or in a sixth step interposed between the third step; step and the fourth step;
• the deposition of the compact film of particles used during the third step is carried out either by a deposition technique involving the air / liquid interface for ordering the particles included in the set formed by the Langmuir Blodgett technique, the Langmuir Shaefer technique, the surface vortic method, the flotation transfer technique, the dynamic and mobile thin laminar flow technique, or by a deposition technique involving only particles in colloidal solution included in the assembly formed by the electrophoretic deposition, the horizontal deposition by evaporation of a film, the deposition by evaporation of a bath, the deposition by vertical withdrawal of a submerged substrate and the horizontal deposition by forced removal the line of contact;
• the dry etching process used in the fourth step is an ionic reactive etching using a gaseous mixture of sulfur hexafluoride (SF ₆ ) and oxygen (O ₂ ) in a ratio of 5/3;
• the etching rate of the substrate material Vsub and the etching rate V by particles, the etch selectivity Sg, defined as the ratio of the etching rate of the substrate to the etching speed of the particles, and the etching time are adjusted to consume all the particles and avoid creating sharp edges on the surface of the substrate;
• the manufacturing method comprises a seventh particle removal step performed after the fourth step.

• .- la Figure 1 est une vue par microscopie électronique à balayage d'une première forme de réalisation d'une surface optique antireflet, micro-structurée selon l'invention, en carbure de silicium SiC polycristallin, obtenue par gravure plasma au travers d'un masque de billes auto-organisées de diamètre 1 micron (µm) ;
• .- la Figure 2 est une vue en coupe dans le sens de leur hauteur et passant leurs sommets de trois microstructures adjacentes de la surface optique antireflet de la Figure 1 ;
• .- la Figure 3 est une vue par microscopie électronique à balayage d'une deuxième forme de réalisation d'une surface optique antireflet, micro-structurée selon l'invention, en carbure de silicium enrichi en silicium SiCSi poly-cristallin, obtenue par gravure plasma au travers d'un masque de billes auto-organisées de diamètre 0,5 micron (µm) ;
• .- la Figure 4 est un ordinogramme général d'un procédé de fabrication d'une surface optique texturée des Figures 1 à 3 suivant un premier mode de réalisation ;
• .- la Figure 5 est un ordinogramme d'un deuxième mode de réalisation d'un procédé de fabrication de la structure de surface texturée des Figures 1 à3;
• .- la Figure 6 une vue d'un mécanisme principal de la gravure sèche mise en oeuvre dans les procédés de fabrication des Figures 1 à 3;
• .- la Figure 7 est une vue des spectres de réflectivité, mesurés dans les domaines visibles et infrarouge pour la surface optique antireflet de la deuxième forme de réalisation de la Figure 3 ;
• .- la Figure 8 est une vue comparative des spectres de réflectivité mesurés dans les domaines visibles et infrarouge pour les surfaces optiques antireflet des première et deuxième formes de réalisation des Figures 1 et 3 ;
• .- la Figure 9 est une vue d'une surface de carbure de silicium SiC, différente de celle de l'invention, ayant des microstructures parasites et obtenue par gravure plasma en l'absence d'utilisation d'un masque de billes de silice auto-organisées ;
• .- la Figure 10 est une vue optique à l'échelle d'une portion d'une surface antireflet de carbure de silicium enrichie SiCSi suivant la deuxième forme de réalisation de la Figure 3, obtenue après une illumination solaire sous 745 W/m² concentrée avec un facteur de concentration 1000 en un spot de concentration de 10 mm de diamètre et une montée en température en ce spot à 676°C ;
• .- la Figure 11 est une vue optique à l'échelle, analogue à celle de la Figure 7, d'une portion d'une surface de molybdène Mo, nano-structurée suivant le procédé de la demande de brevet précité WO 2015/114519 A1 , et obtenue après une illumination solaire sous 810 W/m2 concentrée avec un facteur de concentration 1000 en un spot de concentration de 10 mm de diamètre et l'atteinte d'une température en ce spot de 582°C ;
• .- la Figure 12 est une vue des spectres de réflectivité d'un absorbeur en carbure de silicium enrichi SiCSi dont la surface est structurée suivant la deuxième forme de réalisation de la Figure 3, les spectres étant mesurés avant et après exposition à un rayonnement solaire concentré par une lentille de Fresnel de grossissement 1000 et de dimensions 33x33 cm2 sous 900 W/m2 de radiation solaire incidente ;
• .- la Figure 13 est une vue des spectres de réflectivité dans les domaines du visible et de l'infrarouge d'un absorbeur en carbure de silicium enrichi SiCSi dont la surface est structurée suivant la deuxième forme de réalisation de la Figure 3, les spectres étant mesurés à différents instants lors d'un vieillissement sous air à une température de 1000°C ;
• .- la Figure 14 est une vue de l'évolution de l'absorption solaire d'un absorbeur solaire en carbure de silicium enrichi SiCSi, la surface d'exposition de l'absorbeur étant structurée suivant la deuxième forme de réalisation de la Figure 3 et exposée à l'air à une température de 1000°C;
• .- la Figure 15 est une vue de l'évolution temporelle de l'absorption solaire de deux échantillons d'un absorbeur solaire en carbure de silicium SiC, fabriqués selon le même procédé de fabrication, la surface d'exposition de l'absorbeur étant structurée suivant la première forme de réalisation de la Figure 1 et exposée à l'air à différentes températures ;
• .- la Figure 16 est une vue par microscopie à balayage électronique de l'effet technique de la forme accidentée ou irrégulière et de la petite taille des microstructures parasites de la Figure 9 sur les performances en vieillissement de la surface micro-structurée en termes de modifications de la forme et de la taille des microstructures, le vieillissement sous air étant visualisé après 250 heures à une température permanente de 1000°C ;
• .- la Figure 17 est une vue par microscopie à balayage électronique de l'effet technique de la forme régulière et de taille des microstructures d'une surface selon l'invention des Figures 1 et 3 sur les performances en vieillissement de la surface micro-structurée en termes de modifications de la forme et de la taille des microstructures, le vieillissement sous air étant visualisée après 250 heures à une température permanente de 1000°C ;

The invention will be better understood on reading the description of several embodiments which will follow, given solely by way of example and with reference to the drawings in which:

• .- the Figure 1 is a scanning electron microscopy view of a first embodiment of an antireflection optical surface, micro-structured according to the invention, of polycrystalline SiC silicon carbide, obtained by plasma etching through a self-adhesive ball mask -organized diameter 1 micron (μm);
• .- the Figure 2 is a sectional view in the direction of their height and passing their vertices of three adjacent microstructures of the optical anti-reflective surface of the Figure 1 ;
• .- the Figure 3 is a scanning electron microscopy view of a second embodiment of an antireflection optical surface, micro-structured according to the invention, made of silicon carbide enriched in polycrystalline SiCSi silicon, obtained by plasma etching through a mask of self-organized beads with a diameter of 0.5 micron (μm);
• .- the Figure 4 is a general flow chart of a method of manufacturing a textured optical surface of Figures 1 to 3 according to a first embodiment;
• .- the Figure 5 is a flowchart of a second embodiment of a method of manufacturing the textured surface structure of Figures 1 to3;
• .- the Figure 6 a view of a main mechanism of dry etching implemented in the manufacturing processes of Figures 1 to 3 ;
• .- the Figure 7 is a view of the reflectivity spectra, measured in the visible and infrared domains for the antireflection optical surface of the second embodiment of the Figure 3 ;
• .- the Figure 8 is a comparative view of the reflectivity spectra measured in the visible and infrared domains for the antireflection optical surfaces of the first and second embodiments of Figures 1 and 3 ;
• .- the Figure 9 is a view of a SiC silicon carbide surface, different from that of the invention, having parasitic microstructures and obtained by plasma etching in the absence of use of a mask of self-organized silica beads;
• .- the Figure 10 is an optical view at the scale of a portion of an antireflection surface of silicon carbide SiCSi enriched according to the second embodiment of the Figure 3 , obtained after a solar illumination under 745 W / m ² concentrated with a concentration factor 1000 at a concentration spot of 10 mm in diameter and a rise in temperature at this spot at 676 ° C;
• .- the Figure 11 is an optical view to scale, similar to that of the Figure 7 of a portion of a surface of molybdenum Mo, nano-structured according to the process of the aforementioned patent application WO 2015/114519 A1 , and obtained after a solar illumination under 810 W / m2 concentrated with a concentration factor 1000 at a concentration spot of 10 mm in diameter and reaching a temperature in this spot of 582 ° C;
• .- the Figure 12 is a view of the reflectivity spectra of an SiCSi enriched silicon carbide absorber whose surface is structured according to the second embodiment of the invention. Figure 3 , the spectra being measured before and after exposure to concentrated solar radiation by a Fresnel lens of magnification 1000 and dimensions 33x33 cm2 under 900 W / m2 of incident solar radiation;
• .- the Figure 13 is a view of the reflectivity spectra in the visible and infrared domains of an SiCSi enriched silicon carbide absorber whose surface is structured according to the second embodiment of the invention. Figure 3 the spectra being measured at different times during aging in air at a temperature of 1000 ° C;
• .- the Figure 14 is a view of the evolution of the solar absorption of a solar absorber SiCSi enriched silicon carbide, the exposure surface of the absorber being structured according to the second embodiment of the Figure 3 and exposed to air at a temperature of 1000 ° C;
• .- the Figure 15 is a view of the temporal evolution of the solar absorption of two samples of a SiC silicon carbide solar absorber, manufactured according to the same manufacturing process, the absorber's exposure surface being structured according to the first form realization of the Figure 1 and exposed to air at different temperatures;
• .- the Figure 16 is a scanning electron microscopy view of the technical effect of the uneven or irregular shape and the small size of the parasitic microstructures of the Figure 9 on the aging performance of the micro-structured surface in terms of changes in the shape and size of the microstructures, aging under air being visualized after 250 hours at a permanent temperature of 1000 ° C .;
• .- the Figure 17 is a scanning electron microscopy view of the technical effect of the regular shape and size of the microstructures of a surface according to the invention of Figures 1 and 3 on the aging performance of the micro-structured surface in terms of changes in the shape and size of the microstructures, aging under air being visualized after 250 hours at a permanent temperature of 1000 ° C .;

The invention relates to the geometry of the structuring of silicon carbide-based materials and to its methods of obtaining which make it possible to increase the absorption of solar radiation in a predetermined wavelength range and to dispose of At the same time, an extremely resistant solution, in terms of a high stability of the shapes and dimensions of the microstructures, at high temperature and in a corrosive medium, for example an oxidizing medium such as air.

Following the Figure 1 an antireflection optical surface 2, with absorption in the visible and near infrared range, in particular for solar thermal absorbers, able to operate at high temperatures, comprises a substrate 4, consisting of a thickness e of a first SiC silicon carbide material of first type, that is to say polycrystalline SiC silicon carbide, and having a flat or curved face 6, exposure to light, solar for example.

The optical anti-reflective surface 2 also comprises an assembly 8 of texturing microstructures 12, 14, 16, 18, 20, 22, 24 lining the exposure face 6 of the substrate.

Here, only seven texturing microstructures 12, 14, 16, 18, 20, 22, 24 have been designated by a numerical reference for the sake of simplification of the description.

Each microstructure 12, 14, 16, 18, 20, 22, 24 of texturing is formed by a single protrusion made in the first material, arranged on and in one piece with the substrate 4.

The microstructures 12, 14, 16, 18, 20, 22, 24 have the same shape, with local variations of materials or processes, and the same dimensions; they extend parallel at least locally relative to each other in a local direction, perpendicular to the exposure face 6, here solar, at the location of each microstructure 12, 14, 16, 18, 20, 22, 24.

The microstructures 12, 14, 16, 18, 20, 22, 24 are distributed on the solar exposure face 6 of the substrate 4 in a two-dimensional periodic pattern 32. Here, the shape of the two-dimensional periodic pattern 32 is for example hexagonal compact.

The shape of each microstructure 12, 14, 16, 18, 20, 22, 24 is smooth and regular having a single vertex, 42, 44, 46, 48, 50, 52, 54 and a radius of curvature that continuously varies from the top of the microstructure 12, 14, 16, 18, 20, 22, 24 to the exposure face 6 of the substrate 4.

Following the Figure 2 , a profile 62 of partial section of the assembly 8 of the microstructures, here the three microstructures 24, 12, 18, aligned and adjacent to each other, and the substrate 4 in support, comprises a continuous contour line 66 of the surface 6 of 'exposure.

Following the Figures 1 and 2 , the surface of each microstructure 12, 14, 16, 18, 20, 22, 24 has the same maximum height h, located in a central zone surrounding its top and corresponding to the height of the microstructure 12, 14, 16, 18 , 20, 22, 24, and decreasing from the top to an edge B of a base of the microstructure 12, 14, 16, 18, 20, 22, 24.

The microstructures 12, 14, 16, 18, 20, 22, 24 of texturing are obtained in this example by plasma etching through a mask of self-organized beads having a diameter equal to one micron. The diameter d of a microstructure located respectively below each ball is here correlatively approximately 1 micrometer and the top of the shape of each microstructure 12, 14, 16, 18, 20, 22, 24 can be described here by a half-sphere or a rounded cone or the top of a parabola.

Here and preferably, all adjacent microstructures are joined at their edges at the exposure face, and their joining surface has a point or line of discontinuous curvature.

Alternatively, the adjacent microstructures are not contiguous at their edges at the exposure face, and the junction curve of each microstructure with the exposure face has a discontinuous curvature line.

As a variant, the adjacent microstructures are not contiguous at their edges at the exposure face, and on a neighborhood of the junction curve of each microstructure with the exposure face, the curvature is continuous.

Diameters of 0.5 microns can be used and produce an optical performance similar to that obtained with a diameter of 1 micron. The arrangement of the microstructures 12, 14, 16, 18, 20, 22, 24 in the local plane of the structured surface is periodic like the arrangement of the used ball mat, the periodic pattern of the arrangement being preferably hexagonal compact but could be different.

Following the Figure 1 which is a top view in perspective of the optical selective antireflection surface 2, it is clear that the two-dimensional periodic pattern 32 is hexagonal compact and that the network of microstructures thus formed is a compact network with hexagonal mesh.

Following the Figure 3 and a second embodiment of the invention, an anti-reflective optical surface 102 is structured and elaborated this time in SiC SiC SiS material which, like the anti-reflective Figure 2 comprises silicon carbide SiC, but which is enriched in silicon Si by presenting islands of Si silicon. This second type of SiSiC material is for example obtained by the formation of a porous carbon material from a pyrolysis and then an infiltration A silicon precursor is made at high temperature to form the SiSiC silicon carbide compound. In the case of this second type of material, the structure obtained is similar to that obtained for the silicon carbide SiC of the first type of material of the Figure 1 and results in a compact hexagonal arrangement of structures that can be described by a form of parabolic domes or rounded cones, or even half-spheres whose diameter is here 0.5 micron.

Here on the Figure 3 two regions of the material of the substrate 104 and microstructures 108 lying on the exposure face 106 of the substrate 104 are partially represented. A first zone 152 of silicon carbide SiC is illustrated in the upper left corner of the Figure 3 and a second zone 154 of silicon Si is illustrated in the lower right corner of the Figure 3 which second zone 154 forms a silicon Si island of substrate 104.

It should be noted that the residues of silica beads visible on the top of certain microstructures 108 are not part of said microstructures and that these bead residues will disappear at the end of the manufacturing process because of their consumption by the method of breaking.

In general, an antireflection optical surface according to the invention, with absorption in the visible and near-infrared range, in particular for solar thermal absorbers, able to operate at high temperatures, comprises a substrate consisting of a thickness of a first SiC silicon carbide material, and having a planar or curved exposure face, and a set of texturing microstructures lining the exposure face.

Each microstructure is formed by a single protrusion made in the first material, disposed on and in one piece with the substrate. The microstructures have the same shape and same dimensions, and are distributed on the face of the substrate in a two-dimensional periodic pattern, and the shape of each of each microstructure is smooth and regular having a single vertex and a radius of curvature that varies continuously from the top of the microstructure to the face of the substrate.

The first material based on silicon carbide is comprised in the assembly formed by single crystal silicon carbide SiC, polycrystalline silicon carbide, silicon carbide SiC monocrystalline or polycrystalline, silicon enriched in the form of silicon. islands of silicon Si.

In particular, the surface of each microstructure comprises a portion of the surface of a spherical or elliptical or parabolic cap.

In general and independently of the embodiment of the selective antireflection optical surface, each microstructure has substantially the same base diameter d greater than or equal to 0.3 μm and less than or equal to 5 μm, preferably between 0.5 μm and 2 μm, and the same maximum height h of each microstructure is greater than or equal to 0.5 times the base diameter d and less than or equal to 5 times the base diameter d.

The radius of curvature ρ of each microstructure is greater than or equal to 0.1 μm and distributed around a central value ρ ₀ with a radius of curvature of between 0.25 μm and 1 μm.

In general, the arrangement of the microstructures on the exposure face of the substrate is in the form of a tessellation of elementary microstructure networks, the elementary arrays having the same mesh pattern included in the assembly formed by the meshes hexagonal, square mesh, triangular mesh, and being characterized by a degree of compactness of the microstructures between them.

Following the Figure 4 and a first embodiment, a method 202 for manufacturing the texturing of the anti-reflective optical surfaces as described, for example, in the Figures 1 to 3 comprises a set of steps 204,206,208,210,212.

This method is particularly suitable for the manufacture of solar heat absorbers, the manufactured textured surface being able to operate at high temperatures and / or in an oxidizing environment such as air.

In a first step 204, a substrate is provided consisting of a thickness of a thermally stable first SiC silicon carbide material having a planar or curved exposure face.

In a second step 206, carried out following the first step 204, a set of texturing microstructures lining the face of the substrate is produced.

Each microstructure is formed by a single protrusion made in the first material, and disposed on and in one piece with the substrate.

The microstructures have the same shape and same dimensions, and are distributed over the exposure face of the substrate in a two-dimensional periodic pattern.

The shape of each microstructure is smooth and regular having a single vertex and a radius of curvature that varies continuously from the top of the microstructure to the face of the substrate.

• soit à fournir du carbure de silicium SiC monocristallin ou poly-cristallin, ou
• soit à fournir du carbure de silicium SiC monocristallin ou poly-cristallin, enrichi en silicium sous forme d'îlots de silicium Si.

The first step 204 consists of:

• supplying monocrystalline or polycrystalline SiC silicon carbide, or
• or to provide silicon carbide SiC monocrystalline or polycrystalline, enriched silicon in the form of Si silicon islands.

• soit à comprimer de manière isostatique une poudre de carbure de silicium SIC, ou
• soit à faire croitre du carbure de silicium SiC poly-cristallin, ou
• soit à faire croitre du carbure de silicium SiC monocristallin, ou
• soit à infiltrer du silicium à Si haute température dans une matrice carbonée poreuse.

In a particular way, the first step 204 consists of:

• either isostatically compressing a silicon carbide powder SIC, or
• either to grow polycrystalline SiC silicon carbide, or
• either to grow monocrystalline SiC silicon carbide, or
• or to infiltrate silicon Si at high temperature into a porous carbon matrix.

The second step 206 comprises a third step 208 and a fourth step 210, executed successively.

In the third step, a compact monolayer of masking particles made of a second material is deposited on the surface of the substrate, the second material being included in the assembly formed by silica (SiO ₂ ), polystyrene (PS) or any other material in the form of beads of required size.

In the fourth step 210, the substrate is etched by a dry etching process on the side of the exposure face through interstices existing between the particles,

During the fourth step 210, that is to say at the same time as the dry etching of the substrate, in a fifth step 212 a reduction of the size and shape of the particles by dry etching is implemented.

Following the Figure 5 and a second embodiment derived from the first embodiment, a method 302 for producing an antireflection optical surface, textured for eg for solar thermal absorbers and as described for example in the Figures 1 to 3 , comprises a set of steps 204, 306, 208, 210, 312.

The first step 204 of the method 302 of the Figure 5 is identical to the first step of method 202 of the Figure 4 .

The second step 306 of the method 302 of the Figure 5 comprises like the method 202 of the Figure 4 the third step 208 and the fourth step 210.

The second step 306 of the method 302 of the Figure 5 differs from the method 202 of the Figure 4 in that it comprises a sixth step 312, interposed between the third step 208 and the fourth step 210, in which a reduction in the size and shape of the particles by dry etching is implemented without interaction with the dry etching of the substrate.

Following the Figures 4 and 5 the manufacturing processes 202, 302 comprise a seventh particle removal step 314 performed after the fourth step 210. For example, the seventh step 314 is to clean the textured surface by dipping it into an ethanol bath in the presence of ultrasound for at least 5 minutes.

Following the Figures 4 and 5 , the deposition of the compact particle film implemented during the third step 208 is performed, either by a deposition technique of a first family involving the air / liquid interface for ordering the particles, or by a technique of deposit of a second family involving exclusively particles in colloidal solution.

The first family of particle deposition techniques in a compact film is the whole formed by the method of transferring a monofilm of compacted particles onto a moving liquid carrier, the technique of Langmuir Blodgett, the Langmuir Shaefer technique, the vortic surface method, the flotation transfer technique, the dynamic and mobile thin laminar flow technique.

The second family of deposition of particles in a compact film is the assembly formed by the electrophoretic deposition, the horizontal deposition by evaporation of a film, the deposition by evaporation of a bath, the deposition by vertical withdrawal of a submerged substrate. and horizontal deposition by forced withdrawal from the nip.

The deposited masking beads are preferably in SiO ₂ , but may be of different nature as long as the main parameters of the etching are respected.

The parameters applied to carry out the bead deposits when the method used is the method of transferring a monofilm of particles compacted on a moving carrier liquid and when a textured surface of Figures 1 to 3 is manufactured are described below in the following Table 1. Table 1 Settings Applied value Low Max Diameter of silica particles 1μm or 540nm 0,01μm 10 .mu.m Solvent butanol Concentration 35g / l 10g / l 50g / l Carrier fluid Deionized water Flow of the carrier liquid 400 ml / min 100 ml / min 1000ml / min Particle injection rate 0.5 ml / min 0.01 l / min 3 ml / min Drawing speed 1 cm / min 0.1 cm / min 10 cm / min

Following the Figures 4 and 5 , the dry etching process used in the fourth step 210 is for example an ionic reactive etching using a gas mixture of sulfur hexafluoride (SF ₆ ) and oxygen (O ₂ ) in a 5/3 ratio. Other gases capable of selectively etching the material with respect to the beads may also be used.

In general and independently of the dry etching process used, the etching rate of the substrate material Vmat and the etching rate V with particles are greater than 50 nm per minute, and the etch selectivity Sg, defined as the ratio of the rate of etching of the substrate material on the etching rate of the particles is between 0.5 and 10.

• des billes de silice SiO₂ de 530nm ou 1 µm déposées par voie colloïdale avec flottaison d'une monocouche compacte de billes sur un solvant et report sur le substrat à texturer,
• un réacteur de type « gravure par ion réactifs » RIE (dénommé en anglais Reactive Ion Etching),
• un générateur à la fréquence de 13,56GHz,
• un mélange de gaz de SF₆ et d'O₂,
• des flux de 5sccm pour SF₆ et 3sccm pour O₂,
• une pression de 25mT,
• une puissance de 0.25W/cm² (20W sur une sole de diamètre de 10cm), et
• une température de substrat égale à 50°C.

When a textured surface of Figures 1 to 3 is manufactured, the dry etching process described below can be used. This etching process uses:

• colloidally deposited 530 nm or 1 μm silica SiO ₂ beads with flotation of a compact monolayer of beads on a solvent and transfer to the substrate to be textured,
• a reactive ion etching reactor RIE (referred to as Reactive Ion Etching),
• a generator at the frequency of 13.56GHz,
• a mixture of SF ₆ and O ₂ gas,
• flows of 5sccm for SF ₆ and 3sccm for O ₂ ,
• a pressure of 25mT,
• a power of 0.25 W / cm ² (20W on a 10 cm diameter hearth), and
• a substrate temperature of 50 ° C.

The time of the etching process depends on the type of material used for the substrate and the diameter of the beads used.

When beads having a diameter of 530 nm are used, the etching process time is equal to 600 s for a substrate material of the first type SiC, and equal to 480 s for a substrate material of the second Si SiC type.

In the case of a 1 micron diameter silica ball, the etching process time is multiplied by 2 relative to the 530 nm diameter balls, ie for example 1200 s for a substrate of the first SiC type.

The conditions of the etching processes defined above are optimized conditions for obtaining the selectivity (ratio of the etch rates between the silica bead mask and the SiC or SiSiC type of engraving material) making it possible to obtain a ratio of form of microstructures, defined as the ratio of their height over their width, of approximately 1, that is to say between 0.3 and 5.

Other etch chemistries may be used, particularly fluorochemicals.

Following the Figure 6 , a so-called "ion bombardment" dry etching mechanism is implemented in the manufacturing processes of the Figures 4 and 5 .

According to this mechanism represented by the arrows 322, 324, 326, the ions issuing from the SF ₆ plasma attack the surface of the substrate, which is accessible through the passage gaps existing between the masking balls, in a non-selective and anisotropic manner. The effectiveness of the attack is even higher than the access to the surface of the material through the carpet of balls is easy. On the Figure 6 , the driving arrow lengths 322, 324, 326, proportional to the intensity and efficiency of the plasma etch, decrease from a surface point 330 of the "open sky" substrate to a contact point 332 of the masking ball 328. In a related manner, the ion bombardment etching of the surface of the substrate is accompanied by an etching of the masking by ion erosion of the surface of the masking balls, the erosion of the surface masking beads having an effect on the etching rate. This so-called "ion bombardment" mechanism is at the origin of the shape of the microstructures described in the Figures 1 to 3 .

Thus, the process of Figures 4 and 5 allows to obtain the structuring as described on the Figures 1 to 3 .

The reflectivity spectra obtained from the selective anti-reflective optical surfaces described in particular in the Figures 1 to 3 , are analogous to the spectrum 402 illustrated in Figure 7 , measured for a structuring of SiSiC material. Reflectivity, measured in the visible and near-infrared range, that is to say for wavelengths between 0.3 and 2.5 microns, is greatly reduced, which allows the realization of a powerful solar absorber.

The spectrum measurements were made on the same sample of SiSiC textured surface by a first measuring apparatus which provided a first visible spectrum curve 404, and by a second measuring apparatus which provided a second spectrum curve 406 in the infrared range.

Following the Figure 7 , the reflectivity spectra 404, 406 in the visible and infrared domains show their difference in reflectivity, a low reflectivity or high absorption for a non-transparent thick medium being observed in the visible range, and a relatively high reflectivity or low emissivity according to the law Kirchhoff being observed in the infrared IR field. Here, a solar absorption of 95.9% and an emissivity at 500 ° C of 67% are measured.

Following the Figure 8 the reflectivity spectra of the optical surfaces using SiC and SiSiC materials before and after structuring are combined.

A first spectrum 414 illustrates the evolution of the reflectivity, expressed as a percentage on a linear scale, as a function of the wavelength, expressed in microns on a logarithmic scale, for an untextured raw surface or smooth silicon carbide .

A second spectrum 416 illustrates the evolution of the reflectivity as a function of the wavelength for an SiC antireflection optical surface made of silicon carbide, the SiC antireflection optical surface being textured with a mask of self-organized balls of diameter 0.5. microns (μm).

A third spectrum 418 illustrates the evolution of the reflectivity as a function of the wavelength for a non-textured or smooth raw silicon silicon-SiSiC optical surface.

A fourth spectrum 420 illustrates the evolution of the reflectivity as a function of the wavelength for an SiSiC antireflection optical surface made of silicon carbide silicon carbide, the SiSiC antireflection optical surface being textured with a mask of self-organized diameter balls. 0.5 microns (μm).

The comparison of the second and fourth spectra 416, 420, with the first and third spectra 414, 418, show the sharp decrease in reflectivity and therefore improvement of the absorption in the visible and near-infrared domains for the two types of materials (SiC, SiSiC) based on silicon carbide.

It should be noted that the manufacturing method according to the invention which uses a dry etching has a particular technical effect when the use of a bead mask during the etching step is omitted. Indeed, as shown on the Figure 9 Without a bead mask, small-scale parasitic micro-masking appears on the optical surface based on silicon carbide because of the carbon deposition, this micro-masking being linked to the deposition of carbonaceous molecules from the etching gas and from -products of the etching reaction. This micro-masking has the effect of creating a carpet 432 of parasitic microstructures 434 in the form of needles of a hundred nanometers maximum width on the optical surface 442 thus obtained.

Conversely, in the case of the presence of silica used in the self-organized beads of the mask provided in the manufacturing method according to the invention, oxygen present in the composition of the beads is released during etching and modifies the composition of the reaction products avoiding the accumulation of carbon on the surface of the substrate and thus avoids parasitic micro-masking. This results in the compact hexagonal structure of smooth domes that will have good resistance to oxidation.

The structures of the optical anti-reflective surfaces as described in the Figures 1 to 3 or obtained by the manufacturing processes described in Figures 4 to 6 are very well suited to solar absorbers and have the double advantage of a very good absorption capacity of solar radiation and excellent resistance to oxidation in air or other oxidizing medium.

Following the Figure 10 , an optical view of a sample 452 of an SiSiC enriched silicon carbide antireflection surface according to the second embodiment of FIG. Figure 3 , obtained after a solar illumination under 745 W / m ² concentrated with a concentration factor 1000 at a concentration spot 454 of 10 mm in diameter and a rise in temperature at this spot at 676 ° C, shows that the structure of the surface Silicon carbide enriched with SiSiC silicon does not show any deterioration after exposure at high solar concentration in air at around 700 ° C. The spot of concentration can not be distinguished on this view from the rest of the surface of the sample.

Conversely and following the Figure 11 , an optical view, similar to that of the Figure 10 of a sample 462 of a surface of molybdenum Mo, nano-structured according to the process of the aforementioned patent application WO 2015/114519 A1 , and obtained after a solar illumination under 810 W / m2 concentrated with a concentration factor 1000 in a concentration spot 464 of 10 mm in diameter and reaching a temperature in this spot of 582 ° C, shows that the material of nano-structured molybdenum is oxidized on the surface at the concentration spot 464, distinguishable on the Figure 11 by a lighter shade, and deteriorates very strongly under air.

The structure of the antireflection optical surface 452 according to the second embodiment of the Figure 3 has a better resistance to oxidation than that 462 of the nano-structured molybdenum of the Figure 11 which presents cracks and delaminations under the effect of its oxidation in the air.

Following the Figure 12 , a first spectrum 472 and a second spectrum 474 of reflectivity of an SiSiC enriched silicon carbide absorber whose surface is structured according to the second embodiment of the invention. Figure 3 are illustrated. The first and second spectra 472, 474 are respectively the spectra measured before and after exposure to concentrated solar radiation by a Fresnel lens of magnification 1000 and dimensions 33 × 33 cm 2 under 900 W / m 2 of incident solar radiation.

The first and second spectra 472, 474 confirm the very good resistance to oxidation of the structured absorbers according to the invention, the two reflectivity spectra before and after the solar exposure being superposable.

Following the Figure 13 , reflectivity spectra, 481, 482, 483, 484, 485, 486, 487, 488, measured in the visible and infrared domains of an SiCSi enriched silicon carbide absorber whose surface is structured according to the second embodiment of the Figure 3 , is illustrated. The spectra 481, 482, 483, 484 in the visible range, respectively the spectra 485, 486, 487, 488 are measured at different respective times, 0 hours, 3 hours, 15 hours, 25 hours, during aging under air at a temperature of 1000 ° C.

The Figure 13 confirms the integrity of the structured absorbers according to the invention for extremely high aging temperatures of the order of 1000 ° C., in air, with spectra in the visible range 481, 482, 483, 484 and in the infrared range 485, 486, 487, 488 unchanged between 0 and 25 hours.

Following the Figure 14 , the temporal evolution 492 of the measured solar absorption of an SiSiC enriched silicon carbide solar absorber whose exposure surface is structured according to the second embodiment of the invention. Figure 3 is illustrated, the aging taking place at a temperature of 1000 ° under air. It appears that the solar absorption and through it the reflectivity parameter remains virtually unchanged over time for extreme temperatures and confirms the excellent performance in service life of structured absorbers according to the invention.

Following the Figure 15 , the temporal evolution 502 of the measured solar absorption of two samples of a silicon carbide solar absorber SiC whose exposure surface is structured according to the first embodiment of the invention. Figure 1 , is shown, both samples being exposed to air for three high temperatures equal to 800 ° C, 1000 ° C and 1200 ° C.

A first set 504 and a second set 506 of measurement data concern respectively the first and second samples for a temperature of 800 ° C.

A third set 508 and a fourth set 510 of measurement data relate to the first and second samples at a temperature of 1000 ° C.

A fifth set 512 and a sixth set 514 of measurement data relate to the first and second samples for a temperature of 1200 ° C.

The first, second, third, fourth, fifth, sixth data sets 504, 506, 508, 510, 512, 514 confirm excellent resistance to high temperature air oxidation of the solar absorber for structured SiC material. the invention, for example with spherical domes or paraboloid of 0.5 micron or 1 micron in diameter. The absorption performance is here maintained above 95% over time, regardless of the extreme high temperatures considered here for aging.

These excellent properties of lifetimes are obtained thanks to the intrinsic resistance of silicon carbide to oxidation but also to the particular forms of structures produced according to the invention.

Indeed, as shown in Figure 16 , the irregular or irregular shape and the small size of parasitic microstructures 552, such as those of the Figure 9 and representative of the state of the art, are significantly modified during aging after 250 hours under air at a permanent temperature of 1000 ° C while being completely oxidized by a relatively large oxide layer.

Conversely, as shown in Figure 17 , the regular shape (spherical, soft conical, parabolic) and the relatively large size of the microstructures of a surface according to the invention of Figures 1 and 3 allow microstructures 562 to substantially maintain the same shape and size by being slightly oxidized at the surface. Thus the optical property of low reflectivity / high absorption is maintained under extreme conditions of temperature and oxidizing medium.

• .- les absorbeurs solaires sélectifs,
• .- les systèmes comprenant des absorbeurs sélectifs de formes par exemple planes ou cylindriques.

The possible applications of the invention relate in particular to:

• selective solar absorbers,
• the systems comprising selective absorbers of shapes, for example flat or cylindrical.

Claims (17)

Antireflection optical surface, with absorption in the visible and near infrared range, in particular for solar thermal absorbers, able to operate at high temperatures, and comprising
a substrate (4; 104), consisting of a thickness of a first SiC silicon carbide material, and having a planar face (6; 106) or exposure curve, and
an assembly (8) of texturing microstructures (12, 14, 16, 18, 20, 22; 108) covering the face (6; 106),
said antireflection optical surface being characterized in that
each microstructure (12, 14, 16, 18, 20, 22, 108) is formed by a single protrusion made in the first material, disposed on and in one piece with the substrate (4; 104), and
the microstructures (12, 14, 16, 18, 20, 22, 108) have the same shape and dimensions, and are distributed on the face (6; 106) of the substrate (4; 104) in a two-dimensional periodic pattern, and
the shape of each microstructure (12, 14, 16, 18, 20, 22, 108) is smooth and regular having a single vertex and a radius of curvature which varies continuously from the top of the microstructure (12, 14, 16, 18, 20, 22, 108) to the face (6; 106) of the substrate (4; 104). An anti-reflective optical surface according to claim 1, wherein the first silicon carbide material is
monocrystalline or polycrystalline SiC silicon carbide, or
SiC monocrystalline or polycrystalline silicon carbide, enriched in silicon in the form of Si silicon islands. An anti-reflective optical surface according to any one of claims 1 to 2, wherein
the surface of each microstructure (12, 14, 16, 18, 20, 22, 108) has a same maximum in height h located in a central zone and corresponding to the height of the microstructure (12, 14, 16, 18, 20 , 22; 108) and decreasing from the top to an edge B of a base of the microstructure (12, 14, 16, 18, 20, 22, 108). Anti-reflective optical surface according to any one of claims 1 to 3, wherein
the surface of each microstructure (12, 14, 16, 18, 20, 22, 108) comprises a portion of the surface of a spherical, elliptical or parabolic cap. An anti-reflective optical surface according to any one of claims 1 to 4, wherein
each microstructure (12, 14, 16, 18, 20, 22, 108) has substantially the same base diameter d greater than or equal to 0.3 μm and less than or equal to 5 μm, preferably between 0.5 μm and 2 μm. μm, and
the same maximum height h of each microstructure (12, 14, 16, 18, 20, 22, 108) is greater than or equal to 0.5 times the base diameter d and less than or equal to 1.5 times the base diameter d. An anti-reflective optical surface according to any one of claims 1 to 5, wherein
the radius of curvature of each microstructure (12, 14, 16, 18, 20, 22, 108) is greater than or equal to 0.1 μm and distributed around a central value with a radius of curvature of between 0.25 μm and 1 μm. An anti-reflective optical surface according to any one of claims 1 to 6, wherein
the arrangement of the microstructures (12, 14, 16, 18, 20, 22; 108) on the exposure side of the substrate is in the form of a tessellation of elementary arrays (60; 70) of microstructures,
the elementary arrays having the same mesh pattern included in the set formed by the hexagonal mesh, the square mesh, the triangular mesh, and being characterized by a degree of compactness of the microstructures between them. Solar absorber comprising an antireflection optical surface defined according to one of Claims 1 to 7. Process for manufacturing an optical antireflection surface, in particular for solar thermal absorbers, able to operate at high temperatures,
said manufacturing process comprising
a first step (204) of providing a substrate, consisting of a thickness of a first SiC silicon carbide material, and having a planar or curved exposure face,
characterized in that it further comprises
a second step (206; 306), performed following the first step, consisting in producing a set of texturing microstructures lining the face,
each microstructure being formed by a single protrusion made in the first material, and disposed on and in one piece with the substrate, and
the microstructures having the same shape and same dimensions, being distributed on the face of the substrate in a two-dimensional periodic pattern, and
the shape of each microstructure being smooth and regular having a single vertex and a radius of curvature that varies continuously from the top to the face. A method of manufacturing an antireflection surface according to claim 9, wherein
the first step (204) consists of: supplying monocrystalline or polycrystalline SiC silicon carbide, or or to provide silicon carbide SiC monocrystalline or polycrystalline, enriched silicon in the form of Si silicon islands. A method of manufacturing an antireflection surface according to any one of claims 9 to 10, wherein
the first step (204) consists of: either isostatically compressing a silicon carbide powder SIC, or either to grow polycrystalline SiC silicon carbide, or either to grow monocrystalline SiC silicon carbide, or or to infiltrate silicon at high temperature in a porous carbon matrix. A method of manufacturing an antireflection surface according to any one of claims 9 to 11, wherein
the second step (206; 306) comprises the successive steps of
in a third step (208) depositing a compact monolayer of particles into a second material on the surface of the substrate, and
in a fourth step (210) etching by a dry etching process the substrate on the side of the exposure face through interstices existing between the particles,
the second material being included in the assembly formed by silica (SiO ₂ ), polystyrene (PS) or any other material in the form of beads of required size. A method of manufacturing an antireflection surface according to claim 12, wherein
a reduction in the size and shape of the particles by dry etching is carried out,
in a fifth step (212) executed during the fourth step (210) together with the dry etching of the substrate,
or in a sixth step (312) interposed between the third step (208) and the fourth step (210). A method of manufacturing an antireflection surface according to any one of claims 12 to 13, wherein
the deposition of the compact particle film implemented during the third step (208) is carried out
either by a deposition technique involving the air / liquid interface to order the particles included in the set formed by the Langmuir Blodgett technique, the Langmuir Shaefer technique, the surface vortical method, the flotation transfer technique, the technique of dynamic and mobile thin laminar flow,
or by a deposition technique exclusively involving particles in colloidal solution comprised in the assembly formed by the electrophoretic deposition, the horizontal deposition by evaporation of a film, the deposition by evaporation of a bath, the deposition by vertical shrinkage. a submerged substrate and the horizontal deposition by forced withdrawal of the line of contact. A method of manufacturing an antireflection surface according to any one of claims 12 to 14, wherein
the dry etching process implemented in the fourth step (210) is an ionic reactive etching using a gaseous mixture of sulfur hexafluoride (SF ₆ ) and oxygen (O ₂ ) in a ratio of 5/3. A method of manufacturing an antireflection surface according to claim 15, wherein
the etching rate of the substrate material Vsub and the etching velocity V by particles, the etch selectivity Sg, defined as the ratio of the etching rate of the substrate to the etching rate of the particles, and the etching time are set from to consume all the particles and avoid the creation of sharp edges on the surface of the substrate. A method of manufacturing an antireflection surface according to any one of claims 12 to 16, comprising a seventh particle removal step (314) performed after the fourth step (210).

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